The offer is good at participating locations and is only good on their Original Chili Cheese Fries, which features an order of French fries topped with Wienerschnitzel's signature chili and shredded cheddar cheese. They normally go for around $2 or so. You can find my previous review of the fries here.
The hot dog chain introduced four new varieties of chili cheese fries earlier this year but none of them are eligible for the deal.